New OLED lighting panel hopes to outshine fluorescent bulbs

At the very least, the future looks bright for OLED lighting.

A helical arrangement of Philips Lighting's GL350 OLED panels, on display at Light + Building 2012 in April.

Philips Lighting

With the arrival of its OLED lighting panel, the Lumiblade GL350, Philips Lighting is attempting to quietly usher in the era of practical OLED lighting. The diminutive squares, 3.3mm thick with edges not even five inches (they're precisely 124.5mm) in length, put out 120 lumens each. As organic light-emitting diodes go, that's really rather punchy. It's this higher output that has led the Dutch electronics giant to declare the GL350 "the first OLED that is suitable for general lighting purposes" in its product catalog.

But can output alone justify the claim? Ars delved into the specs of the OLED panel, which Philips unveiled to dramatic effect at the Light + Building trade show in Frankfurt in April. We spoke to Iain Macrae, president of the Society of Light and Lighting and head of Global Lighting Application Management at light fitting manufacturer Thorn Lighting, about the broader state of play in OLED illumination.

Empty the contents of a pack of GL350s, and you'll find three OLED panels which, if placed end to end, would stretch 373.5 mm (14.7 inches) in length and deliver a total output of 360 lumens. Compare that to a 300mm (foot-long) fluorescent tube which puts out 400 lumens, and it's clear that Philips's claims of viable performance are serious. OK, our improvised OLED strip is longer, wider, and emits less light, but it's in the same ballpark of usefulness.

But Philips isn't relying on output alone to make the case for the GL350, which boasts other impressive specs. First among these is its color temperature of 3250K. If you're not familiar with the concept of color temperature (or, strictly, correlated color temperature), it's an absolute expression of the color of a lamp that uses a black-body radiator (an ideal emitter) as a yardstick. The hotter a black body radiator, the bluer and cooler it appears to glow. The color of a lamp can simply be expressed by quoting the temperature (in kelvin) of the black body radiator it resembles.

Though ideal color temperature is highly subjective (and varies with application), 3250K is a shrewd choice. Being just on the yellow side of white, the GL350 is nearly identical in hue to a halogen lightbulb, which has been a mainstay of interior lighting, and one people are very used to. But achieving warm colors with an OLED hasn't been the technical hurdle it was with LED technology. Really, the 3250K boils down to a marketing decision. The GL350 actually appears cooler than OLED alternatives. Osram's ORBEOS OLEDs are a positively toasty 2800K, similar to other Philips Lumiblade OLEDs.

Perhaps more impressive is the GL350's Color Rendering Index (CRI), which Philips quotes as better than 90 out of a possible 100. Though the color appearance of a light source does affect its ability to accurately render color, color appearance and CRI should not be conflated. For light sources with a color temperature (under 5000K), the color rendering performance of a light source is directly compared to a black body radiator at that temperature. For light sources with color temperature above 5000K, daylight is the basis for comparison.

Truly ready to shine?

An incandescent light bulb has a CRI of 100 because it is basically as good as a black body radiator at rendering the eight specified colors stipulated by the International Commission on Illumination (CIE). The fact that it's not good at rendering different shades of blue is neither here nor there. It's as good as the yardstick.

"You have to be careful on the CRI scale and new technologies," The Society of Light and Lighting's Iain Macrae told Ars. "Where white light OLED and LED are concerned, there is already a question if the use of RGB color mixing is less suited to the current measure. The CIE are currently looking at more appropriate measures based on research. CRI is of course important for domestic and workplace lighting; generally, a CRI above 80 is considered minimum good practice. New technology doesn't change the way we see. The eye hasn't evolved in line with technology. Color rendering is still important to being able to see well, just the measure may need to change."

Ideally, for a lamp to accurately render color, it will have both a high CRI and the color temperature of daylight—5000 to 6000K. The upshot of the GL350's CRI combined with its color temperature is that its color-rendering performance should be much the same as halogen lighting.

But there is a problem with Philips's claims of the practicality of the GL350. It has a power consumption of 7.2W. That may not sound much, but the light source emits a meager 120 lumens, giving a lumen efficacy of only 16.7lm/W. This suffers in comparison to energy-saving light sources such as fluorescent lighting and LEDs, where certain products achieve efficacies over (and in LED's case, well over) 100lm/W. The latest compact fluorescent light bulbs weigh in at between 50 and 70lm/W.

The GL350's performance is poor even by OLED standards. Philips's own Lumiblade PLUS OLED panel achieves 45lm/W, though its output per unit area is only one quarter that of the GL350's. In fact, an efficacy of 16.7lm/W is firmly within incandescent territory, and had international lighting legislation focused more on performance targets than on banning specific technologies, the GL350 might never have emerged. It certainly falls well short of the minimum efficacy of 45lm/W for general-purpose lighting, set to come into effect in 2020 in the US.

Looking through the lens of efficiency, it's hard to justify the claim that the GL350 is the first OLED suitable for general lighting. "I would have still put [OLED] in its innovation stage. It is not stable enough, efficient enough, or low enough cost to become mainstream yet," Macrae told Ars, when asked for his take on the general state of OLED lighting today. "Our brand specifically would not adopt a technology until it can outperform the existing technology on a number of levels," he added, speaking with his Thorn Lighting hat on. "I think energy efficiency has to be balanced with sustainability, where OLED will have benefits, but also on cost, useful light, and on practicality. Compared to LED and to fluorescent, OLED technology is simply not efficient enough for our customers, but there will be early adopters who see other values, making it worthwhile."

Reason for optimism

Having said that, Macrae shares the industry's broader optimism for the possibilities OLED technology presents, which we reported on last year. "The technology could allow the window glass to be lit, the walls too, the ceiling even, but as complete surfaces or decorative panels," he said. "It should push the market away from the ceiling-mounted regular arrays of luminaries we currently see." Though Macrae points out that for such developments to occur, some innovations in power supply are necessary.

If the future of OLED lighting really is glowing walls and ceilings, then Philips would appear to be barking up the wrong tree by producing small, bright panels that compete for the same market niche as traditional light sources. Though the GL350 is doubtless a noteworthy evolutionary step in the development of OLED lighting, it is larger, lower output surfaces we're waiting for (and besides, LEDs have the small-bright thing covered).

Whatever form OLED lighting eventually takes, more efficiency is required. Philips is optimistic. "Moving forward, we expect efficacy of our Lumiblade OLED panels in our decorative line to reach 35 lm/W by 2018," a Philips spokesman told Ars. "For our Lumiblade OLED performance line we expect to attain an efficacy level of 130 lm/W by 2018." (It's interesting that by this metric, Philips would seem to be positioning the GL350 as decorative rather than general purpose lighting.)

In the near future, Macrae's preference is for polymer light-emitting diodes (PLEDs), a subset of OLED technology in which the electroluminescent layer is a polymer, such as a polyfluorene derivative. "OLED potentially offers colored lighting options, but requires a difficult manufacturing process, so it's less sustainable," he told Ars. "PLED can effectively be printed with less impact on the environment, but is generally a white light source. I prefer the latter as it's more applicable to most applications, and long-term sustainability is vital."

Though it seems likely that OLED will join LED as the predominant light sources of the future, it appears that, in OLED's case at least, the future isn't here just yet.

Promoted Comments

The explanation of CRI, it's affect on colour, and how things are viewed just left me baffled. I don't understand what a black body radiator is, except that incandescent bulbs are almost as good as them (at whatever it is they do).

It's quite simple once you get it - as with everything

A black body radiator is a theoretical construct. The black body part means it does not reflect any light (or any electromagnet waves), so it would always look pitch black. That's the theoretical part...Now take a soldering lamp and heat a piece of iron wire. You will see it starts glowing red, then yellow, then whitish while melting into drops. The simplified principle is that matter of a certain temperature emits electromagnetic waves. The higher the temp, the higher the frequency (the shorter the wave length).Now when you heat something up further and further, the emitted radiation grows from low infrared (which is sensed as heat) to high infrared, to red, to yellow...

So if you now think about that a black body radiator is basically a non reflecting piece of matter at a certain temperature it should be obvious why an incandescent light bulb is so close to the theoretical optimum. It is just a piece of matter that's very hot.

Of course there's good reason to choose exactly the idea of a black body radiator as a measurement. The stars, one of them being our prime source of light, work basically like this, as they also emit light as a result of being hot.

Also of course the details are a bit more complicated as there isn't just one wavelength emitted but a spectrum of a characteristic form and there's also interesting stuff with Kirchhoff's Law and why nothing else could emit more radiation than a black body etc bla blaBut for a basic understanding you don't need that.

Concerning the OLED panels:Someone said here it would be a research project that makes some money en passant.I agree. I can't see any real use yet besides rich people who crave anything that's expensive and modern and some artists that work with light in creative ways. For anything else it seems useless or far overpriced.

From years of experiences using a high temperature soldering torch. A mixture of oxygen and natural gas. I know from the outer layer of the cone-shaped flames have the color of blue and the inner-cone are white which is the hottest point you can get from a burning torch. The tip of the white flame can get up to as hot as 3 to 5,000 degree Fahrenheit, maybe higher, depends on the mixture of the chemicals.

So to speak, the outer-layers of the blue flames are far less hot as the white flames.

We see red/orange flames coming from a burning house but those flames are not as hot-hot. Not even close to the temperature of the blue flames. So red flames have the lowest temperature amongst the blue and white flames.

The point for Philips is the absolute brightness. These panels appear to deliver about 8,000 NITs (lumens per square meter) and that, for OLED, is pretty darn bright. A good bright computer monitor is about 300 NITs, which is also about what you get on an AMOLED cellphone.

So, while this is not the most efficient it is still good efficiency and the absolute brightness makes it practical, for the first time, to have enough light from the panel to light up a room. If you take a look at how much effort in a typical office environment goes into designing the lumieres to diffuse the light to make the experience more pleasant, and then consider that these tiles do the same thing right out of the box, you can see this offers some new possibilities for designers. Philips probably expects this leading edge product to be used for niche designs where this advantage is appreciated.

Most other OLEDs would die after minutes or hours at such output levels.

I hope OLED lighting turns out good! Replacing bulbs with extremely thin, shaped panels would be a whole new way to think about light. For instance, just imagine how many shapes Amazon will soon carry...

Thanks for the primers on K° and CR index. It thickles me when packaging only says "cool white" or "soft white" or "daylight"; when enough people ask for the actual specs, it will be labelled appropriately.

You don't put the degree symbol when referencing kelvins. The degree symbol indicates an arbitrary zero point, where as kelvins has an absolute zero point.

The degree symbol says the units of measure are degrees. Fahrenheit & Celsius degrees are measured as distance from a zero point above Absolute Zero, so you may find a leading minus sign in addition to the degree symbol. The F, C, R or K can replace the degree symbol specifying which of the 4 major scales are being used.F & R degrees are the same unit. The difference between Fahrenheit & Rankin is the positioning of 0 on the scale.C & K degrees are the same unit. The difference between Celsius & Kelvin is the positioning of 0 on the scale.

In order to promote confusion a thermal unit exactly equal to a C or K degree is called the Kelvin. Temperatures can be measured by counting the Kelvins in the temperature measurement. This number is identical to the number of Kelvin/Celsius degrees above absolute zero. When measuring temperatures with Kelvins the degree symbol is omitted and the word Kelvin is spelled out. When measuring temperatures with the Kelvin scale, one of the degree symbol or K is included to denote a temperature measurement in degrees.

The ISO standard deprecates the Kelvin temperature scale in favor of counting Kelvins.Centigrade is an earlier metric temperature scale almost exactly the same as Celsius. These two are normally considered interchangeable.

From someone who is having to plaster some cracks in his ceiling (and finding the whole process to be a pain in the @$$) I find the idea of expensive glowing ceilings interesting and horrifying. My kids would break the ceiling with a careless flung shoe or a good thunderstorm might pull up shingles and spring a small leak which could frazzle the whole thing.

"The technology could allow the window glass to be lit, the walls too, the ceiling even, but as complete surfaces or decorative panels,"

You know what would be the perfect product? Drop ceiling panels! Get rid of the large tube sets or seemingly out of place pot lamps and just make 2'x2' OLED panels that can drop right into an existing ceiling arrangement.

Love that. How does it compare to the billions of incandescent lights still in use today? Also how long does it last?

For lighting innovators, this is a awesome launch. There's no doubt these can place light where its needed, and from that point, reducing overall consumption as compared to any lighting source could be excellent.

Also using these in areas where light has to be extremely bright to reach could be of high value.

Finally, I wonder if there's a shape shifting method of customization that would allow unique applications to be designed. spherical segments? Interior box corners?